Buried junction enhanced Schottky barrier device

ABSTRACT

A Schottky barrier device having a completely submersed Schottky barrier junction to enhance the collection efficiency of photogenerated carriers. A method is also disclosed for manufacturing the device.

STATEMENT OF GOVERNMENT INTEREST

The invention described herein may be manufactured and used by or forthe Government for governmental purposes without the payment of anyroyalty thereon.

BACKGROUND OF THE INVENTION

The present invention relates generally to infrared detector devices,and in particular to such a detector utilizing a completely submersedSchottky barrier junction.

When a metal is brought into intimate contact with a semiconductorsurface, the resulting metallic semiconductor surface exhibits currentrectifying characteristics. Such an interface is commonly referred to asa Schottky barrier device and acts in a similar fashion to a p-nsemiconductor junction. Such Schottky barrier devices are well known andhave been extensively reported and utilized.

It is also known to build up an array of Schottky barrier devices forinfrared sensing, and combining the array with a charge coupled diodereadout system for achieving an infrared camara device vidicon system.Such a Schottky diode array is disclosed in U.S. Pat. No. 3,902,066,issued to Sven A. Roosild et al. on Aug. 26, 1975.

Present Schottky infrared charge coupled diode (IRCCD) arrays have lowquantum efficiencies (sensitivities) thus limiting their applicationsfor certain thermal imaging scenarios.

It is therefore an object of the present invention to provide animproved Schottky IRCCD device of improved sensitivity and quantumefficiency.

It is a further object of the present invention to provide a method formanufacturing such a device.

SUMMARY OF THE INVENTION

The present invention contemplates a completely submersed Schottkybarrier junction in order to enhance collection efficiency ofphotogenerated carriers. Using a buried active back-to-back thinjunction allows collection of carriers generated with momentum vectorsin both the forward and reverse directions. Thus, the quantum efficiencyand sensitivity of the infrared detector is substantially enhanced. Inaddition, thicker Schottky metalliations can be used to enhance spectralabsorption of incident infrared lights.

BRIEF DESCRIPTION OF THE DRAWING

The foregoing and other advantages, objects and features of thisinvention will become apparent from the following description when readin conjunction with the accompanying drawing in which:

FIGS. 1, 2 and 3 illustrate various stages in the formation of theburied Schottky barrier IRCCD device of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 shows a p-type silicon substrate. The substrate has at this stagebeen oxidized for n+ contacts, guard rings and an n channel. After then+ material has been diffused in the substrate the oxides are removed.The channel oxide is then grown. A polysilicon gate (CCD transfer gate)is then defined and polysilicon is deposited for the gate.

Referring now to FIG. 2 of the drawings, a window is now defined for theelectrode or transition metal, which is preferrably platinum, but couldbe other metals such as iridium or palladium for example. The depositedmetal, which is the order of 50 to 100 Angstroms thick, is then sinteredto form the metal silicide diode. Thereafter, the unreacted metal isremoved, a ring is now etched around the diode to expose the p-typesilicon substrate and n+ diffusions.

As shown in FIG. 3 of the drawings, a p-type polysilicon layer is nowdeposited over the exposed substrate. The added layer is then laser orthermally annealed so that a single layer epitaxial layer regrows overthe diode, forming a back-to-back p-Si/MSi/p-Si diode structure.

At this point aluminum can be overcoated over either the front or backsurface of the structure, but not both, to further enhance opticalabsorption via optical reflection.

The key feature of this invention, as described above, is the formationof single crystal silicon on both sides of the Schottky sensingelectrode via laser or thermal annealing, and the associated advantagesof having an embedded electrode for sensing.

Although the invention has been described with reference to a particularembodiment, it will be understood to those skilled in the art that theinvention is capable of a variety of alternative embodiments within thespirit and scope of the appended claims. For example, the inventionapplies to all possible metallic Schottky electrodes and is notrestricted to either platinum silicide or iridium silicide electrodes.

What is claimed is:
 1. A method for manufacturing a buried junctionenhanced Schottky barrier device comprising the steps of:(a) oxidizing ap-type silicon substrate for contacts, guard rings and an n channel; (b)diffusing n+ material in defined areas in the front surface of saidsubstrate; (c) removing oxides from said substrate; (d) defining anddepositing a polysilicon charge transfer gate and gate electrode; (e)defining an area for the transition metal of said device; (f) depositingsaid transition metal and sintering said metal to form a metal-silicondiode; (g) removing unreacted portions of said metal; (h) etching a ringaround said diode to expose said p-type substrate and n+ diffusions; (i)depositing p-type silicon over exposed areas of said substrate and saidmetal silicon diode; and (j) annealing said device whereby a singlelayer epitaxial film regrows over said diode to form a back-to-backp-type silicon/metal/p-type silicon diode structure.
 2. A methodaccording to claim 1 wherein said transition metal is platinum.
 3. Amethod according to claim 1 wherein said transition metal is iridium. 4.A method according to claim 1 wherein said transition metal ispalladium.
 5. A method according to claim 1 wherein said transitionmetal is nickel.
 6. A method according to claim 1 and including theadditional step of:overcoating the front surface of said device withaluminium to enhance its optical absorption characteristics.
 7. A methodaccording to claim 1 and including the additional step of:overcoatingthe back surface of said device with aluminum to enhance its opticalabsorption characteristics.
 8. A buried junction Schottky barrier devicecomprising:a semiconductor substrate; a metal deposited on saidsubstrate to form a first metal-semiconductor interface; a semiconductormaterial disposed over the exposed surface of said metal to form asecond metal-semiconductor interface; and means for deriving signalsfrom said first and second metal-semiconductor interface.
 9. Apparatusas defined in claim 8 wherein said metal is platinum and saidsemiconductor substrate is p-type silicon.
 10. Apparatus as defined inclaim 8 and further comprising:a layer of aluminum disposed over asurface of said substrate to enhance optical absorption of saidapparatus.